Conventional, oil recovery involves drilling a well and pumping a mixture of oil and water from the well. Oil is separated from the water and the water is usually injected into the subsurface formation. Conventional recovery works well for low viscosity oil. However, conventional oil recovery processes do not work well for higher viscosity, or heavy oil.
Enhanced oil recovery processes employ thermal methods to improve the recovery of heavy oils from subsurface reservoirs. The injection of steam into heavy oil bearing formations is a widely practiced enhanced oil recovery method. Typically, several tonnes of steam are required for each tonne of oil revered. Steam heats the oil in the reservoir, which reduces the viscosity of the oil and allows the oil to flow to a collection well. After the steam fully condenses and mixes with the oil, the condensed steam is classified as produced water. The mixture of oil and produced water that flows to the collection well is pumped to the surface. Oil is separated from the water by conventional processes employed in conventional oil recovery operations.
Steam assisted gravity drainage (SAGD) provides is a relatively new oil recovery process for producing heavy oil, which ideally utilizes 100% quality steam for injection into well (i.e., no liquid water). Once injected into the well, the 100% quality steam transfers heat to the heavy oil upon condensation. The heavy oil with reduced viscosity drains together with steam condensate and is recovered via a producer well, disposed parallel and beneath the injector well.
Other heavy oil recovery methods that utilize steam include cyclic steam stimulation (CSS) and steam flooding.
Steam generation costs limit economic returns of the SAGD, CSS and steam flooding. Relative to conventional boiler or once through steam generation approaches, direct steam generation may facilitate lowering these costs due to improvements in efficiency, inherent makeup water replacement and reduced fouling issues. Direct steam generation operates by burning a fuel in a combustor and quenching resulting combustion products with water to produce a mixture of steam and the combustion products including any unconsumed trace amounts oxygen.
Oxygen mixed in the steam is highly corrosive to the carbon steel materials used in conventional oilfield production systems. Methods for reducing the impact of the presence of oxygen include changing the metallurgy of the facilities to use an oxygen resistant material or utilizing chemical corrosion prevention treatment to coat the exposed surface of carbon steel. However, such methods may have high capital cost and potentially limited benefit at high temperatures.
Therefore, a need exists for removing trace levels of oxygen from the mixture of steam and combustion products.